The class of cyclic enones is well known in organic chemistry. Best known examples of cyclic enones are quinones such as, for example, the benzoquinones, naphthoquinones, anthraquinones, phenanthraquinones, and the like. 1,4-Benzoquinone is commonly referred to as quinone. Quinones are generally brightly colored compounds and have versatile applications in chemical synthesis, biological uses, as redox materials, as well as in industry. There are several review articles on the chemistry and applications of quinones including, for example, Kirk-Othmer Encyclopedia of Chemical Technology, Third ed., Vol. 19, pages 572-605, John Wiley & Sons, New York, 1982. The synthesis of quinones is well documented. See, for example, J. Cason, Synthesis of Benzoquinones by Oxidation, in Organic Synthesis, Vol. IV, page 305, John Wiley & Sons, New York (1948). Quinones generally are prepared by oxidizing the appropriately disubstituted aromatic hydrocarbon derivatives, the substituents being hydroxyl or amino groups in the ortho or para positions. 1,4-benzoquinone, for example, can be made from the oxidation of hydroquinone, p-aminophenol or p-phenylenediamine, or from quinic acid. The reagents generally used for the oxidation are dichromate/sulfuric acid mixture, ferric chloride, silver (II) oxide or ceric ammonium nitrate. In these cases, oxidation of the aminoaromatic compound is accompanied by hydrolysis to the corresponding quinone. Some processes may take several hours for completion of the reaction.
Thus, certain prior art processes utilize a catalytic agent to achieve an acceptable reaction while other processes proceed without catalysts. The process according to the present invention utilizes a metal or metal salt oxidation catalyst which provides high conversion and reaction rates to prepare the quinonediimine.
A prior art process, which utilizes a catalyst in the preparation of a quinoneimine compound, is disclosed by Desmurs, et al. in U.S. Pat. No. 5,189,218. The process of Desmurs, et al., which converts N-(4-hydroxyphenyl)aniline into N-phenylbenzoquinone-imine, utilizes a manganese, copper, cobalt, and/or nickel compound as a catalyst in an oxidation type reaction. Although Desmurs, et al. identify converting the N-phenylbenzoquinone-imine into an N-phenyl-N'-cycloalkyl-2,5-cyclohexadine-1,4-diimine, Desmurs, et al. fails to recognize the use of an oxidation catalyst for the conversion, much less a metal oxidation catalyst, as used in the present invention. This is evidenced by Desmurs, et al. suggestion at col. 5, lines 14-22, to use a hydrogenation catalyst.
Other processes are known which use oxidizing agents to convert phenylenediamines into their corresponding quinonediimines. For example, EP 708,081 (Bernhardt et al), which describes the conversion of phenylenediamines to phenylenediimines by oxidation of the diamine in an alkali/alcoholic solution, gives a general description of such processes in its background. The EP '081 process suffers from various disadvantages including long reaction times and low yields.
Additional oxidation conversion processes are described by Wheeler in U.S. Pat. No. 5,118,807, by GB1,267,635 and by Haas et al, in EP 708,080. However, the use of oxygen along with a metal catalyst or salt of a metal catalyst in the conversion of phenylenediamine compounds to give highly selective yields of quinonediimine compounds has not heretofore been suggested.
As such, the current invention is based on the problem of providing a simple and economic process for the preparation of quinonediimines in high yields and with high purity.